Method for reporting mobility information in wireless communication system and apparatus for supporting same

ABSTRACT

Provided is a method for reporting mobility information by means of a terminal in a wireless communication system. The method includes generating mobility information and reporting the mobility information via a network. The mobility information includes mobility state information indicating the estimated mobility state of the terminal, and mobility history information relating to the mobility history of the terminal.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to wireless communications, and moreparticularly, to a method of reporting mobility information of a userequipment in a wireless communication system, and an apparatussupporting the method.

2. Related Art

3^(rd) generation partnership project (3GPP) long term evolution (LTE)evolved from a universal mobile telecommunications system (UMTS) isintroduced as the 3GPP release 8. The 3GPP LTE uses orthogonal frequencydivision multiple access (OFDMA) in a downlink, and uses singlecarrier-frequency division multiple access (SC-FDMA) in an uplink. The3GPP LTE employs multiple input multiple output (MIMO) having up to fourantennas. In recent years, there is an ongoing discussion on 3GPPLTE-advanced (LTE-A) evolved from the 3GPP LTE.

A micro cell, a femto cell, and a pico cell, etc., having a smallservice coverage may be installed in a specific location within acoverage of a macro cell having a wide coverage. Such a cell may becalled a small cell.

Since a user equipment (UE) which is a representative mobile devicemoves, quality of a currently provided service may deteriorate or a cellcapable of providing a better service may be detected. Accordingly, theUE may move to a new cell, which is called performing a movement of theUE.

Each cell has a fixed service coverage, and the UE moves on a wirelesscommunication system at a variable speed. Therefore, how often the UEmoves from one cell to another may change occasionally. In order tosupport a proper inter-cell movement of the UE by considering an actualmovement situation of the UE, a method of a mobility state estimation(MSE) and of scaling a mobility parameter has been supported.

With the deployment of cells having various sizes in a wirelesscommunication system, an area in which a network can utilize informationregarding a mobility of the UE becomes much wider. For this, it isrequested to provide a method in which the UE reports the mobilityinformation to the network.

SUMMARY OF THE INVENTION

The present invention provides a method of reporting mobilityinformation in a wireless communication system, and an apparatus forsupporting the method.

In an aspect of the present invention, a method for mobility informationreporting performed by a terminal in a wireless communication system isprovided. The method comprises generating mobility information; andreporting the mobility information to a network. The mobilityinformation comprises mobility state information indicating an estimatedmobility state of the terminal and mobility history information relatedto a history of performing a movement of the terminal.

The generating of the mobility information may comprise estimating themobility state and collecting at least one mobility history entry,wherein the mobility history information comprises the at least onemobility history entry.

Each of the mobility history entries may be collected when the terminalperforms the movement through a cell reselection or a handover.

Each of the mobility history entries may comprise a cell identity foreach serving cell, a time during which the terminal stays in each of theserving cells and a time at which the terminal moves to each of theserving cells.

Each of the mobility history entries may further comprise the number ofserving cells experienced by the terminal during a previous specifictime period from a time at which the terminal moves to each of theserving cells.

Each of the serving cells may be a new serving cell on the basis of themovement performed by the terminal.

Each of the serving cells may be a previous serving cell on the basis ofthe movement performed by the terminal.

Each of the mobility history entries may be collected when a mobilityinformation generation is allowed for each of the serving cells.

Each mobility history entry may be discarded when a specific time periodelapses from a collection time.

The maximum number of the reported at least one mobility history entrymay be a positive integer N.

If the number of collected mobility history entries exceeds N, a firstcollected mobility history entry may be replaced by a most recentlycollected mobility history entry.

The method may further comprise discarding the mobility information ifthe mobility information is reported.

The reporting of the mobility information may comprise transmitting amobility information availability indicator for indicating a presence ofmobility information to be reported by the terminal and upon receiving amobility information reporting request from the network in response tothe mobility information availability indicator, transmitting themobility information to the network.

The mobility information availability indicator may be transmittedduring a process in which the terminal configures a radio resourcecontrol (RRC) connection with the network.

The mobility information may be reported to the network during a processin which the terminal configures an RRC connection with the network.

In another aspect of the present invention, a terminal operating in awireless communication system is provided. The terminal comprises aradio frequency (RF) unit for transmitting and receiving a radio signaland a processor operatively coupled to the RF unit. The processor isconfigured for: generating mobility information; and reporting themobility information to a network, wherein the mobility informationcomprises: mobility state information indicating an estimated mobilitystate of the terminal; and mobility history information related to ahistory of performing a movement of the terminal.

According to an embodiment of the present invention, a user equipment(UE) collects information related to performing a movement and reportsit to a network. Since the UE optionally reports mobility information tothe network, the network can more effectively estimate a state relatedto the movement of the UE. On the basis thereof, the network can providea configuration related to an operation of the UE, and thus may providea more improved service to the UE. In addition, a network resource canbe more effectively used.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a wireless communication system to which the presentinvention is applied.

FIG. 2 is a block diagram illustrating a radio protocol architecture fora user plane.

FIG. 3 is a block diagram illustrating a radio protocol architecture fora control plane.

FIG. 4 is a flowchart illustrating an operation of a UE in an RRC idlestate.

FIG. 5 is a flowchart illustrating a procedure of establishing an RRCconnection.

FIG. 6 is a flowchart illustrating a procedure of reconfiguring the RRCconnection.

FIG. 7 is a drawing illustrating the procedure of the RRC connectionre-establishment.

FIG. 8 is a flowchart showing the conventional method of performing ameasurement.

FIG. 9 shows an example of a measurement configuration configured to auser equipment (UE).

FIG. 10 shows an example of deleting a measurement identity.

FIG. 11 shows an example of deleting a measurement object.

FIG. 12 is a flowchart showing a method of reporting mobilityinformation according to an embodiment of the present invention.

FIG. 13 is a block diagram of a wireless device according to anembodiment of the present invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

FIG. 1 illustrates a wireless communication system to which the presentinvention is applied. This may also be called an evolved-UMTSterrestrial radio access network (E-UTRAN) or a long term evolution(LTE)/LTE-A system.

The E-UTRAN includes a base station (BS) 20 that provides a controlplane and a user plane to a user equipment (UE) 10. The UE 10 may befixed or movable and may be called other terms such as a mobile station(MS), a user terminal (UT), a subscriber station (SS), a mobile terminal(MT), a wireless device, and the like. The base station 20 represents afixed station that communicates with the UE 10, and may be called otherterms such as an evolved-NodeB (eNB), a base transceiver system (BTS),an access point, and the like.

The base stations 20 may be connected to each other through an X2interface. The base station 20 is connected with an evolved packet core(EPC) 30 through an S1 interface, in more detail, a mobility managemententity (MME) through an S1 MME and a serving gateway (S-GW) through anS1-U.

The EPC 30 is constituted the MME, the S-GW, and a packet data networkgateway (P-GW). The MME has access information of the UE or informationon a capability of the UE, and the information is primarily used formobility management of the UE. The S-GW is a gateway having the E-UTRANas an end point and the P-GW is a gateway having a PDN as the end point.

Layers of a radio interface protocol between the UE and a network may bedivided into an L1 (first layer), an L2 (second layer), and an L3 (thirdlayer) based three lower layers of an open system interconnection (OSI)reference model which is widely known in a communication system andamong them, a physical layer that belongs to the first layer provides aninformation transfer service using a physical channel and a radioresource control (RRC) layer positioned on the third layer serves tocontrol radio resources between the UE and the network. For this, theRRC layer exchanges an RRC message between the UE and the base station.

FIG. 2 is a block diagram illustrating a radio protocol architecture fora user plane. FIG. 3 is a block diagram illustrating a radio protocolarchitecture for a control plane. A data plane is a protocol stack foruser data transmission and the control plane is a protocol stack fortransmitting a control signal.

Referring to FIGS. 2 and 3, a physical (PHY) layer provides theinformation transfer service to an upper layer by using the physicalchannel. The physical layer is connected with a medium access control(MAC) layer as an upper layer through a transport channel. Data movebetween the MAC layer and the physical layer through the transportchannel. The transport channel is classified depending on a transmissionmethod and a transmission feature through a radio interface.

Data move between different physical layers, that is, between physicallayers of a transmitter and a receiver through the physical channel. Thephysical channel may be modulated by orthogonal frequency divisionmultiplexing (OFDM) and uses a time and a frequency as the radioresource.

A function of the MAC layer includes mapping between a logic channel andthe transport channel, and multiplexing/demultiplexing to a transportblock provided to the physical channel onto the transport channel of anMAC service data unit (SDU) that belongs to the logic channel. The MAClayer provides a service to a radio link control (RLC) layer through thelogic channel.

A function of the RLC layer includes concatenation, segmentation, andreassembly of an RLC SDU. In order to assure various quality of services(QoS) requested by a radio bearer (RB), the RLC layer provides threeoperating modes of a transparent mode (TM), an unacknowledged mode (UM),and an acknowledged mode (AM). An AM RLC provides error correctionthrough an automatic repeat request (ARQ).

The radio resource control (RRC) layer is defined only on the controlplane. The RRC layer serves to control the logic channel, the transportchannel and the physical channels in association with configuration,re-configuration, and release of radio bearers. The RB means a logicroute provided by the first layer (PHY layer) and the second layers (theMAC layer, the RLC layer, and the PDCP layer) in order to transfer databetween the UE and the network.

A function of a packet data convergence protocol (PDCP) layer on theuser plane includes transferring of user data, header compression, andciphering. A function of a packet data convergence protocol (PDCP) layeron the user plane includes transferring of control plane data andciphering/integrity protection.

Setting the RB defines features of the radio protocol layer and channelin order to provide a specific service and means a process of settingrespective detailed parameters and operating methods. The RB may bere-divided into two types of a signaling RB (SRB) and a data RB (DRB).The SRB is used as a passage for transmitting the RRC message on thecontrol plane and the DRB is used as a passage for transmitting the userdata on the user plane.

When an RRC connection is established between the RRC layer of the UEand the RRC layer of the E-UTRAN, the UE is in an RRC connected stateand if not, the UE is in an RRC idle state.

A downlink transport channel for transmitting data from the network tothe UE includes a broadcast channel (BCH) for transmitting systeminformation and besides, the downlink transport channel includes adownlink shared channel (SCH) for transmitting user traffic or a controlmessage. Traffic or a control message of a downlink multicast orbroadcast service may be transported through the downlink SCH ortransported through an additional downlink multicast channel (MCH).Meanwhile, an uplink transport channel for transporting data from the UEto the network includes a random access channel (RACH) for transportingan initial control message and besides, an uplink shared channel (SCH)for transporting the user traffic or control message.

The logical channel that is positioned on the transport channel andmapped to the transport channel includes a broadcast control channel(BCCH), a paging control channel (PCCH), a common control channel(CCCH), a multicast control channel (MCCH), a multicast traffic channel(MTCH), and the like.

The physical channel is constituted by a plurality of OFDM symbols in atime domain and a plurality of sub-carriers in a frequency domain. Onesub-frame is constituted by the plurality of OFDM symbols in the timedomain. A resource block as a resource allocation unit is constituted bythe plurality of OFDM symbols and the plurality of sub-carriers.Further, each sub-frame may use specific sub-carriers of specific OFDMsymbols (e.g., a first OFDM symbol) of a corresponding sub-frame for thephysical downlink control channel (PDCCH), that is, an L1/L2 controlchannel. A transmission time interval (TTI) is a unit time oftransmitting the sub-frame.

Hereinafter, the RRC state and the RRC connection method of the UE willbe described in detail.

The RRC state represents whether the RRC layer of the UE is logicallyconnected with the RRC layer of the E-UTRAN and a case in which both RRClayers are logically connected to each other is called the RRCconnection state and a case in which both RRC layers are not logicallyconnected to each other is called the RRC idle state. Since the RRCconnection exists in the UE in the RRC connection state, the E-UTRAN maydetermine the existence of the corresponding UE by the unit of a cell tothereby effectively control the UE. On the contrary, the E-UTRAN may notdetermine the UE in the RRC idle state and a core network (CN) ismanaged by the unit of a tracking area which a region unit larger thanthe cell. That is, it is determined whether the UE in the RRC idle stateexists by the unit of a large region, and the UE needs to move to theRRC connection state in order to receive a general mobile communicationservice such as voice or data.

When a user first turns on a power supply of the UE, the UE firstretrieves an appropriate and thereafter, the UE stays in the RRC idlestate in the corresponding cell. The UE in the RRC idle stateestablishes the RRC connection with the E-UTRAN through an RRCconnection procedure at least when the UE in the RRC idle state needs tomake the RRC connection, and is transited to the RRC connections state.Cases in which the UE in the RRC idle state needs to make the RRCconnection are various, and for example, uplink data transmission isrequired due to a user's call attempt or when a paging message isreceived from the E-UTRAN, the cases may include response messagetransmission thereto.

A non-access stratum layer (NAS) located above the RRC layer performsfunctions such as session management and mobility management.

In order to manage mobility of the UE on the NAS layer, two states ofEPS mobility management (EMM)-REGISTERED and EMM-DEREGISTERED aredefined and both states are applied to the UE and the MME. An initial UEis in the EMM-DEREGISTERED state and the UE performs a process ofregistering the initial UE in a corresponding network through an initialattach procedure in order to access the network. When the attachprocedure is successfully performed, the UE and the MME are in theEMM-REGISTERED state.

In order to manage a signaling connection between the UE and the EPC,two states of an EPS connection management (ECM)-IDLE state and anECM-CONNECTED state are defined and both states are applied to the UEand the MME. When the UE in the ECM-IDLE state makes the RRC connectionwith the E-UTRAN, the corresponding UE is in the ECM-CONNECTED state.When the MME in the ECM-IDLE state makes an S1 connection with theE-UTRAN, the MME is in the ECM-CONNECTED state. When the UE is in theECM-IDLE state, the E-UTRAN does not have context information of the UE.Therefore, the UE in the ECM-IDLE state performs a UE based mobilityassociated procedure such as cell selection or cell reselection withoutthe need for receiving a command of the network. On the contrary, whenthe UE is in the ECM-CONNECTED state, the mobility of the UE is managedby the command of the network. When the position of the UE in theECM-IDLE state is different from a position which the network knows, theUE notifies a corresponding position of the UE to the network through atracking area update procedure.

Next, the system information will be described.

The system information includes required information which the UE needsto know to access the base station. Therefore, the UE needs to receiveall of the system information before accessing the base station andfurther, the UE continuously needs to have latest system information. Inaddition, since the system information is information which all UEs inone cell need to know, the base station periodically transmits thesystem information.

According to Phrase 5.2.2 of 3GPP TS 36.331 V8.7.0 (2009-09) “RadioResource Control (RRC); Protocol specification (Release 8)”, the systeminformation is divided in to a master information block (MIB), ascheduling block (SB), and a system information block (SIB). The MIBallows the UE to know a physical component, for example, a bandwidth.The SB allows the UE to know transmission information of the SIBs, forexample, a transmission period, and the like. The SIB is an aggregate ofassociated system information. For example, any SIB includes onlyinformation on a neighboring cell and any SIB includes only informationon an uplink wireless channel used by the UE.

In general, a service which the network provides to the UE may bedivided into three types. Further, the UE differently recognizes even atype of the cell by considering which service the UE receives. Theservice type will be first described below and thereafter, the type ofthe cell will be described.

1) Limited service: The service may provide an emergency call and anearthquake and Tsunami warning system (ETWS), and provide the emergencycall and the earthquake and Tsunami warning system (ETWS) in anacceptable cell.

2) Normal service: The service may mean a public use general service andmay provide the public use general service in a suitable or normal cell.

3) Operator service: The service may mean a service for a communicationnetwork operator and only the communication network operator may use thecell and a general user may not use the cell.

The type of the cell may be divided as below in association with theservice type provided by the cell.

1) Acceptable cell: Cell where the UE may receive the limited service.The cell is a cell that is not barred in terms of the corresponding UEand satisfies a cell selection criterion of the UE.

2) Suitable cell: Cell where the UE may receive the suitable service.The cell satisfies a condition of the acceptable cell andsimultaneously, satisfies additional conditions. As the additionalconditions, the cell needs to belong to a public land mobile network(PLMN) which the corresponding UE may access and needs to be a cellwhere execution of the tracking area update procedure of the UE is notbarred. When the corresponding cell is the CSG cell, the correspondingcell needs to be a cell where the UE may access the cell as a CSGmember.

3) Barred cell: The cell is a cell where information indicating that thecorresponding cell is a cell barred through the system information isbroadcasted.

4) Reserved cell: The cell is a cell where information indicating thatthe corresponding cell is a cell reserved through the system informationis broadcasted.

FIG. 4 is a flowchart illustrating an operation of a UE in an RRC idlestate. FIG. 4 illustrates a procedure of registering a UE of whichinitial power is turned on in the network through a cell selectionprocess and thereafter, cell reselection is performed as necessary.

Referring to FIG. 4, the UE selects radio access technology (RAT) forcommunicating with the public land mobile network from which the UEitself intends to receive the service (step, S410). Information on thePLMN and the RAT may be selected by a user of the UE and the informationstored in a universal subscriber identity module (USIM) may be used.

The UE selects a cell having a largest value among cell having measuredlarger signal intensity or quality than specific values (cell selection)(step, S420). The UE of which power is turned on performs the cellselection and the execution of the cell selection may be called initialcell selection. A cell selection procedure will be described below indetail. After the cell selection, the UE receives the system informationwhich the base station periodically sends. The aforementioned specificvalue represents a value defined in the system in order to receive anassurance for quality of a physical signal in transmitting/receivingdata. Therefore, the value may vary depending on the applied RAT.

When network registration is required, the UE performs a networkregistration procedure (step, S430). The UE registers its owninformation (e.g., IMSI) in order to receive a service (e.g., paging)from the network. The UE does not register the information in theaccessed network whenever selecting the cell, and registers theinformation when information (e.g., a tracking area identity; TAI) ofthe network that receives from the system information is different frominformation on a network known by the UE.

The UE performs the cell reselection based on a service environmentprovided by the cell or an environment of the UE (step, S440). When avalue of measured intensity or quality of the signal from a base stationfrom which the UE receives the service is smaller than a value measuredfrom a base station of a neighboring cell, the UE selects one of othercells that provide a more excellent signal feature than the cell of thebase station accessed by the UE. This process is distinguished from theinitial cell selection as Process No. 2 to be cell re-selection. In thiscase, a temporal constraint is given in order to prevent the cell frombeing frequently reselected with the variation of the signal feature. Acell selection procedure will be described below in detail.

FIG. 5 is a flowchart illustrating a procedure of establishing an RRCconnection.

The UE sends to the network an RRC connection request message forrequesting the RRC connection (step, S510). The network sends an RRCconnection setup message as a response to the RRC connection request(step, S520). The UE enters an RRC connection mode after receiving theRRC connection setup message.

The UE sends to the network an RRC connection setup complete messageused to verify successful completion of establishing the RRC connection(step, S530).

FIG. 6 is a flowchart illustrating a procedure of reconfiguring the RRCconnection. The RRC connection reconfiguration is used to modify the RRCconnection. The RRC connection reconfiguration is used for perform RBestablishment/modification/release, handover, and measurementsetup/modification/release.

The network sends to the UE an RRC connection setup message formodifying the RRC connection (step, S610). The UE sends to the networkan RRC connection reconfiguration complete message used to verifysuccessful completion of establishing the RRC connection reconfigurationas a response to the RRC connection reconfiguration (step, S620).

Hereinafter, the public land mobile network (PLMN) will be described.

The PLMN is a network that is deployed and operated by mobile networkoperators. Each mobile network operator operates one or more PLMN. EachPLMN may be distinguished by Mobile Country Code (MCC) and MobileNetwork Code (MNC). The PLMN information of cells is included in thesystem information and broadcasted.

For selecting PLMN, cells and reselecting cells, various types of PLMNsmay be considered by a UE.

HPLMN (Home PLMN): The PLMN having MCC and MNC which are respectivelymatched to MCC and MNC of a UE IMSI.

EHPLMN (Equivalent HPLMN): The PLMN handled to be equivalent to theHPLMN.

RPLMN (Registered PLMN): The PLMN of which the location is successfullyregistered.

EPLMN (Equivalent PLMN): The PLMN handled to be equivalent to the RPLMN.

Each consumer of the mobile service subscribes to the HPLMN. When thegeneral service is provided for a UE through the HPLMN or the EHPLMN,the UE is not in the roaming state. On the other hand, a service isprovided for a UE through the PLMN except the HPLMN/EHPLMN, the UE is inthe roaming state, and the PLMN is called Visited PLMN (VPLMN).

When the power of the UE is turned on at an initial stage, the UEretrieves the public land mobile network (PLMN) and selects anappropriate PLMN capable of receiving the service. The PLMN is a networkthat is deployed or operated by a mobile network operator. Each mobilenetwork operator operates one or more PLMNs. Each of the PLMNs may beidentified by a mobile country code (MCC) and a mobile network code(MNC). The PLMN information of the cell is included in the systeminformation and broadcasted. The UE attempts to register the selectedPLMN. When the registration is succeeded, the selected PLMN becomes aregistered PLMN (RPLMN). The network may signal a PLMN list to the UEand the PLMNs included in the PLMN list may be considered as the PLMNsuch as the RPLMN. The UE registered in the network needs to bereachable by the network. When the UE is in the ECM-CONNECTED state(similarly, the RRC connection state), the network recognizes that theUE receives the service. However, when the UE is in the ECM-IDLE state(similarly, the RRC idle state), a situation of the UE is not effectivein the eNB, but the situation is stored in the MME. In this case, theposition of the UE which is in the ECM-IDLE state is known to only theMME as granularity of a list of tracking areas (TAs). A single TA isidentified by a tracking area identity configured by the PLMN identityto which the TA belongs and the tracking area code (TAC) uniquelyexpressing the TA in the PLMN.

Subsequently, the UE selects a cell having signal quality and feature toreceive an appropriate service among cells provided by the selectedPLMN.

Next, the procedure of a UE selecting a cell will be described indetail.

When power is turned on or being remained in a cell, the UE performs theprocedures to be serviced by selecting/reselecting a cell of adequatequality.

The UE in the RRC idle state should select the cell of adequate qualityalways and be ready for being serviced through the cell. For example,the UE which is just turned on should select a cell of adequate qualityin order to register a network. When the UE in the RRC connection stateenters the RRC idle state, the UE should select the cell which is goingto remain in the RRC idle state. As such, the procedure of selecting acell satisfying a certain condition in order for the UE to remain in theservice standby state such as the RRC idle state is called the CellSelection. It is an important point to select the cell as quick aspossible, since the cell selection is performed in the state that thecell where the UE remains in the RRC idle state is not yet determined.Accordingly, if the cell provides a high level of wireless signalquality, the cell can be selected in the procedure of cell selectionalthough the cell is not a cell that provides the best wireless signalquality.

Now, with reference to 3GPP TS 36.304 V8.5.0 (2009-03) “User Equipment(UE) procedures in idle mode (Release 8)”, the method and procedure thata UE select a cell in 3GPP LTE will be described.

The cell selection process is generally divided into two ways.

First, as an initial cell selection process, the UE has no advanceinformation on the radio channel during this process. Therefore, the UEretrieves all radio channels in order to find the appropriate cell. TheUE finds the strongest cell in each channel. Thereafter, the UE selectsthe corresponding cell only at the time of finding the suitable cellthat satisfies the cell selection criterion.

Next, the UE may select the cell by using stored information or usinginformation broadcasted in the cell. Therefore, the cell selection maybe rapidly performed as compared with the initial cell selectionprocess. When the UE only finds the cell that satisfies the cellselection criterion, the UE selects the corresponding cell. When the UEdoes not find the suitable cell that satisfies the cell selectioncriterion through such a process, the UE performs the initial cellselection process.

After the UE selects a predetermined cell through the cell selectionprocess, the strength or quality of the signal between the UE and thebase station may be changed due to the mobility of the UE or a change ofa wireless environment. Therefore, when the quality of the selected celldeteriorates, the UE may select other cell that provides higher quality.When the cell is again selected as such, a cell that provides highersignal quality than the currently selected cell is generally selected.The process is referred to as the cell reselection. The cell reselectionprocess generally has a basic object to select the cell having thehighest quality to the UE.

In addition to the quality of the radio signal, the network decides apriority for each frequency to notify the priority to the UE. The UEthat receives the priority preferentially considers the priority to aradio signal quality criterion during the cell reselection process.

There may be a method for selecting or reselecting the cell according tothe signal feature of the wireless environment and there may be a cellreselection method described below according to the features of the RATand the frequency of the cell.

-   -   Intra-frequency cell reselection: The UE reselects a cell having        the same RAT and the same center-frequency as a cell which is        being camping.    -   Inter-frequency cell reselection: The UE reselects a cell having        the same RAT and a different center-frequency as the cell which        is being camping.    -   Inter-RAT cell reselection: The UE reselect a cell using an RAT        different from an RAT which is being camping.

A principle of the cell reselection process will be described below.

First, the UE measures the qualities of the serving cell and theneighboring cell for the cell reselection.

Second, the reselection is performed based on the cell reselectioncriterion. The cell reselection criterion has features described belowin association with the measurement of the serving cell and theneighboring cell.

The intra-frequency cell reselection is basically based on ranking. Theranking defines an index value for evaluating the cell reselection andthe cells are ordered in the order of the index value by using the indexvalue. A cell having the best index is generally called a best rankedcell. The cell index value is based on a value which the UE measures forthe corresponding cell and is applied with a frequency offset or a celloffset as necessary.

The inter-frequency cell reselection is based on a frequency priorityprovided by the network. The UE attempts to camp on a frequency havingthe highest frequency priority. The network may provide the frequencypriority to which UEs in cell will commonly apply through broadcastsignaling or provide a frequency-dedicated priority for each UE throughUE-dedicated signaling. The cell reselection priority provided throughthe broadcast signaling may be called the common priority, and the cellreselection priority setup by the network for each UE may be called thededicated priority. When the UE receives the dedicated priority, the UEmay receive the relevant validity time together with the dedicatedpriority. When the UE receives the dedicated priority, the UE starts thevalidity timer which is setup as the relevant validity time. The UEapplies the dedicated priority in the RRC idle mode while the validitytimer is operating. If the validity timer is terminated, the UE discardsthe dedicated priority and applies the common priority again.

The network may provide a parameter (e.g., a frequency-specific offset)used for the cell reselection to the UE for the inter-frequency cellreselection for each frequency.

The network may provide a neighboring cell list (NCL) used for the cellreselection to the UE for the intra-frequency cell reselection or theinter-frequency cell reselection. The NCL includes a cell-specificparameter (e.g., cell-specific offset) used in the cell reselection.

The network may provide a cell reselection black list used for the cellreselection to the UE for the intra-frequency cell reselection or theinter-frequency cell reselection. The UE does not perform the cellreselection for a cell included in the black list.

Subsequently, the ranking performed during the cell reselectionevaluating process will be described.

A ranking criterion used for giving the priority of the cell is definedas illustrated in Equation 1.

R _(s) =Q _(meas,s) +Q _(hyst) ,R _(n) =Q _(meas,n) −Q_(offset)  [Equation 1]

Herein, R_(s) represents a ranking criterion of the serving cell, R_(n)represents a ranking criterion of the neighboring cell, Q_(meas,s)represents a quality value which the UE measures for the serving cell,Q_(meas,n) represents a quality value which the UE measures for aneighboring cell, Q_(hyst) represents a hysteresis value for theranking, and Q_(offset) represents an offset between two cells.

In an intra-frequency, when the UE receives an offset Q_(offsets,n)between the serving cell and the neighboring cell,Q_(offoset)=Q_(offsets,n) and when the UE does not receiveQ_(offsets,n), Q_(offset)=0.

In an inter-frequency, when the UE receives the offset Q_(offsets,n) forthe corresponding cell, Q_(offset)=Q_(offsets,n)+Q_(frequeney) and whenthe UE does not receive Q_(offsets,n), Q_(offset)=Q_(frequeney).

When the ranking varies while the ranking criterion Rs of the servingcell and the ranking criterion of the neighboring cell R_(n) are similarto each other, the ranking is frequently reversed, and as a result, theUE may alternatively reselect both cells. Q_(hyst) represents aparameter for preventing the UE from alternatively reselecting bothcells by giving hysteresis in cell reselection.

The UE measures the R_(s) of the serving cell and the R_(n) of theneighboring cell according to the above equation and regards a cellhaving the largest ranking criterion value as the best ranked cell andreselects this cell.

According to the criterion, it can be seen that the quality of the cellacts as the most important criterion in the cell reselection. If thereselected cell is not the suitable cell, the UE excludes thecorresponding frequency or the corresponding cell from a cellreselection target.

Hereinafter, a radio link monitoring (RLM) will be described.

A UE monitors DL quality based on the cell-specific reference signal inorder to detect the DL wireless link quality of the PCell. The UEestimates DL wireless link quality for monitoring the DL wireless linkquality of the PCell and compares it with the threshold values Qout andQin. The threshold value Qout is defined with the level in which the DLwireless link cannot be stably received, and it corresponds to 10% blockerror rate of hypothetical PDCCH transmission considering the PDFICHerror rate. The threshold value Qin is defined with the level in whichthe DL wireless link can be stably received, better than the level ofthe Qout, and it corresponds to 2% block error rate of hypotheticalPDCCH transmission considering the PCFICH error rate.

Hereinafter, a radio link failure (RLF) will be described.

The UE performs continuously performs measurement for the quality of aradio link with the serving cell that receives the service. The UEdecides whether communication is impossible under a current situationdue to deterioration in quality of the radio link with the serving cell.When the communication is almost impossible due to too low quality ofthe serving cell, the UE decides the current situation as a wirelessconnection failure.

When a radio link failure is decided, the UE abandons maintainingcommunication with a current serving cell, selects a new cell throughthe cell selection (alternatively, cell reselection) procedure, andattempts RRC connection re-establishment to a new cell.

In the specification of 3GPP LTE, the cases which are not able to do thenormal communication are exemplified as follows.

-   -   The case that the UE determines that there is a serious problem        in the downlink communication link quality based on the radio        quality measurement result of the physical layer of the UE (The        case of determining that the quality of the PCell is low during        performing the RLM).    -   The case that the UE determines that there is a problem in the        uplink transmission since the random access process continuously        fails on the MAC sub layer.    -   The case that the UE determines that there is a problem in the        uplink transmission since the uplink data transmission        continuously fails on the RLC sub layer.    -   The case that the UE determines that the handover fails.    -   The case that the message received by the UE does not pass the        integrity check.

Hereinafter, the process of the RRC connection re-establishment will bedescribed in more detail.

FIG. 7 is a drawing illustrating the procedure of the RRC connectionre-establishment.

Referring to FIG. 7, the UE interrupts the use of all radio bearerswhich was configured except for the Signaling Radio Bearer #0, andinitializes all sorts of sub layers of access stratum (AS). In addition,each sub layer and physical layer is configured as defaultconfiguration. During this process, the UE maintains the RRC connectionstate.

The UE performs the cell selection process for performing the RRCconnection re-establishment process (step, S720). Although the UEmaintains the RRC connection state, the cell selection process may beperformed identically to the cell selection process that the UE performsin the RRC idle state.

The UE determines whether the corresponding cell is proper by verifyingthe system information of the corresponding cell after performing thecell selection process (step, S730). If it is determined that theselected cell is a proper E-UTRAN cell, the UE transmits the RRCconnection re-establishment message to the corresponding cell (step,S740).

Meanwhile, if the cell selected through the cell selection process forperforming the RRC connection re-establishment process is determined tobe the cell that uses different RAT except the E-UTRAN, the RRCconnection re-establishment process is interrupted, and the UE entersthe RRC idle state (step, S750).

The UE may be implemented to complete the verification of thesuitability of the cell within a limited time through the cell selectionprocess and receiving the system information of the selected cell. Forthis, the UE may drive a timer in accordance with the start of the RRCconnection re-establishment process. The timer may be interrupted if itis determined that the UE selects a proper cell. When the timer isterminated, the UE may enter the RRC idle state by regarding the RRCconnection re-establishment as failed. The timer will be referred to asthe radio link failure timer below. In the LTE specification TS 36.331,the timer whose name is T311 may be utilized as the radio link failuretimer. The UE may acquire the setting value of the timer from the systeminformation of the serving cell.

When receiving the RRC connection re-establishment request message fromthe UE and accepting the request, the cell transmits the RRC connectionre-establishment message to the UE.

The UE that receives the RRC connection re-establishment message fromthe cell reconfigures the PDCP sub layer for SRB1 and the RLC sub layer.In addition, the UE recalculates all sorts of key values related to thesecurity setting and reconfigures the PDCP sub layer that is in chargeof the security as newly calculated security key values. Through this,SRB1 is open between the UE and the cell and the RRC control message maybe exchanged. The UE completes the start of SRB1, and transmits the RRCconnection re-establishment complete message which is that the RRCconnection re-establishment process is completed to the cell(S760).

Meanwhile, if the cell receives the RRC connection re-establishmentrequest message and does not accept the request, the cell transmits aRRC connection reestablishment reject message to the UE.

When the RRC connection re-establishment process is successfullyperformed, the cell and the UE perform the RRC connectionreconfiguration process. Through this, the UE recovers the state priorto performing the RRC connection re-establishment process, andguarantees the continuity of the service as much as possible.

Next, the description related to RLF reporting will be followed.

In order to support the mobility robustness optimization (MRO) ofnetwork, when the RLF occurs or the handover failure occurs, the UEreports such failure event to the network.

After the RRC connection re-established, the UE may provide the RLFreport to the eNB. The radio measurement included in the RLF report maybe used for identifying the coverage problems as a potential reason offailure. The information may exclude such events in the MRO evaluationfor the intra-LTE mobility connection failure, and may use the eventsfor the input of other algorithms.

When the RRC connection re-establishment is failed or the UE is unableto perform the RRC connection re-establishment, the UE reconnects in theidle mode, and then may generate the effective RLF report for the eNB.For this purpose, the UE may save the latest RLF or the informationrelated to the handover failure, and may indicate the LTE cell that theRLF report is valid at every RRC connection (re)establishment and thehandover until the RLF report is loaded by the network or for 48 hoursafter the RLF or handover failure is detected.

The UE maintains the information for the state shift and change of theRAT, and indicates again that the RLF report is valid after going backto the LTE RAT.

The validity of the RLF report in the RRC connection configurationprocedure is that the UE undergoes the disturbance such as a connectionfailure and indicates that the RLF report hasn't been yet transferred tothe network due to the failure. The RLF report from the UE includes thefollowing information.

-   -   The last cell that has provided service to the UE (in case of        the RLF) or the E-CGI of the target of handover. If the E-CGI is        not known, the PCI and the frequency information are used        instead of it.    -   The E-CGI of the cell that tried the re-establishment.    -   The E-CGI of the cell that provides service to the UE when the        last handover is initialized, for example, when the message 7        (the RRC connection reconfiguration) is received by the UE.    -   The time lapsed from the last handover initialization to the        connection failure.    -   The information indicating whether the connection failure is due        to the RLF or the handover failure.    -   The radio measurements.    -   The location of failure.

The eNB that receives the RLF failure from the UE may forward the reportto the eNB that has provided service to the UE before the connectionfailure reported. The radio measurements included in the RLF report maybe used for identifying the coverage issues which are the potentialcauses of the radio link failure. The information may exclude the eventsfrom the MRO evaluation of the intra-LTE mobility connection failure andmay be used to resend them as the input for other algorithm.

Hereinafter, a measurement and a measurement report are described.

It is necessary for a mobile communication system to support a mobilityof a UE. Therefore, the UE persistently measures quality of a servingcell providing a current service and quality of a neighbor cell. The UEreports a measurement result to a network at a proper time. The networkprovides an optimal mobility to the UE by using a handover or the like.A measurement for such a purpose is often referred to as a radioresource management (RRM) measurement.

To provide information which can be helpful for a network operation of avender in addition to the purpose of supporting the mobility, the UE mayperform a measurement with a specific purpose determined by the network,and may report the measurement result to the network. For example, theUE receives broadcast information of a specific cell determined by thenetwork. The UE may report to a serving cell a cell identity (alsoreferred to as a global cell identity) of the specific cell, locationidentification information of the specific cell (e.g., a tracking areacode), and/or other cell information (e.g., whether it is a member of aclosed subscriber group (CSG) cell).

If a UE in motion determines that quality of a specific area issignificantly bad, the UE may report a measurement result and locationinformation on cells having bad quality to the network. The network mayattempt to optimize the network on the basis of the measurement resultreported from UEs which assist the network operation.

In a mobile communication system having a frequency reuse factor of 1, amobility is generally supported between different cells existing in thesame frequency band. Therefore, in order to properly guarantee themobility of the mobility of the UE, the UE has to properly measure cellinformation and quality of neighbor cells having the same centerfrequency as a center frequency of a serving cell. A measurement on acell having the same center frequency as the center frequency of theserving cell is referred to as an intra-frequency measurement. The UEperforms the intra-frequency measurement and reports a measurementresult to the network, so as to achieve the purpose of the measurementresult.

A mobile communication vendor may operate a network by using a pluralityof frequency bands. If a service of a communication system is providedby using the plurality of frequency bands, an optimal mobility can beguaranteed to the UE when the UE is able to properly measure cellinformation and quality of neighbor cells having a different centerfrequency from the center frequency of the serving cell. A measurementon a cell having the different center frequency from the centerfrequency of the serving cell is referred to as an inter-frequencymeasurement. The UE has to be able to perform the inter-frequencymeasurement and report a measurement result to the network.

When the UE supports a measurement on a network based on a differentRAT, a measurement on a cell of the network may be performed accordingto a configuration of a BS. Such a measurement is referred to as aninter-radio access technology (RAT) measurement. For example, the RATmay include a GMS EDGE radio access network (GERAN) and a UMTSterrestrial radio access network (UTRAN) conforming to the 3GPPstandard, and may also include a CDMA 2000 system conforming to the3GPP2 standard.

FIG. 8 is a flowchart showing the conventional method of performing ameasurement.

A UE receives measurement configuration information from a BS (stepS810). A message including the measurement configuration information isreferred to as a measurement configuration message. The UE performs themeasurement based on the measurement configuration information (stepS820). If a measurement result satisfies a reporting condition includedin the measurement configuration information, the UE reports themeasurement result to the BS (step S830). A message including themeasurement result is referred to as a measurement report message.

The measurement configuration information may include the followinginformation.

(1) Measurement object information: This information is in regards to anobject for which a measurement is performed by the UE. The measurementobject includes at least one of an intra-frequency measurement objectwhich is an object of an intra-frequency measurement, an inter-frequencymeasurement object which is an object of an inter-frequency measurement,and an inter-RAT measurement object which is an object of an inter-RATmeasurement. For example, the intra-frequency measurement object mayindicate a neighbor cell having the same frequency band as a frequencyband of a serving cell, the inter-frequency measurement object mayindicate a neighbor cell having a different frequency band from afrequency band of the serving cell, and the inter-RAT measurement objectmay indicate a neighbor cell having a different RAT from an RAT of theserving cell.

(2) Reporting configuration information: This information is in regardsto a report type and a reporting condition regarding when the UE reportsa measurement result. The reporting configuration information may beconstructed of a list of reporting configurations. Each reportingconfiguration may include a reporting criterion and a reporting format.The reporting criterion is a criterion which triggers the UE to transmita measurement result. The reporting criterion may be a period of ameasurement report or a single event for the measurement report. Thereporting format is information regarding a specific type according towhich the UE configures the measurement result.

(3) Measurement identity information: This information is in regards toa measurement identity for determining when and in what type the UE willreport a specific measurement object by associating the measurementobject with a reporting configuration. The measurement identityinformation may be included in the measurement report message toindicate a specific measurement object for which the measurement resultis obtained and a specific reporting condition according to which themeasurement report is generated.

(4) Quantity configuration information: This information is in regardsto a measurement unit, a reporting unit, and/or a parameter forconfiguring filtering of a measurement result value.

(5) Measurement gap information: This information is in regards to ameasurement gap as a duration that can be used by the UE only for ameasurement without consideration of data transmission with a servingcell when downlink transmission or uplink transmission is not scheduled.

To perform a measurement procedure, the UE has a measurement objectlist, a measurement reporting configuration list, and a measurementidentity list.

In 3GPP LTE, the BS can assign only one measurement object to the UEwith respect to one frequency band. Events for triggering a measurementreport shown in the table below are defined in the section 5.5.4 of 3GPPTS 36.331 V8.5.0 (2009-03) “Evolved Universal Terrestrial Radio Access(E-UTRA) Radio Resource Control (RRC); Protocol specification (Release8)”.

TABLE 1 Events Reporting Condition Event A1 Serving becomes better thanthreshold Event A2 Serving becomes worse than threshold Event A3Neighbor becomes offset better than serving Event A4 Neighbor becomesbetter than threshold Event A5 Serving becomes worse than threshold1 andneighbor becomes better than threshold2 Event B1 Inter RAT neighborbecomes better than threshold Event B2 Serving becomes worse thanthreshold1 and inter RAT neighbor becomes better than threshold2

If the measurement result of the UE satisfies the defined event, the UEtransmits a measurement report message to the BS.

FIG. 9 shows an example of a measurement configuration configured to aUE.

First, a measurement identity1 901 associates an intra-frequencymeasurement object with a reporting configuration 1. The UE performs anintra-frequency measurement. The reporting configuration 1 is used todetermine a report type and a criterion for a measurement result report.

Although a measurement identity2 902 is associated with theintra-frequency measurement object similarly to the measurementidentity1 901, it associates the intra-frequency measurement object witha reporting configuration 2. The UE performs a measurement. Thereporting configuration 2 is used to determine a report type and acriterion for a measurement result report.

By using the measurement identity1 901 and the measurement identity2902, the UE transmits a measurement result even if the measurementresult on the intra-frequency measurement object satisfies any one ofthe reporting configuration 1 and the reporting configuration 2.

A measurement identity3 903 associates an inter-frequency measurementobject 1 with a reporting configuration 3. When a measurement result onthe inter-frequency measurement object 1 satisfies a reporting conditionincluded in the reporting configuration 1, the UE reports themeasurement result.

A measurement identity4 904 associates an inter-frequency measurementobject 2 with the reporting configuration 2. When a measurement resulton the inter-frequency measurement object 2 satisfies a reportingcondition included in the reporting configuration 2, the UE reports themeasurement result.

Meanwhile, the measurement object, the reporting configuration, and/orthe measurement identity can be added, modified, and/or deleted. Toinstruct such operations, the BS may transmit to the UE a newmeasurement configuration message or a measurement configurationmodification message.

FIG. 10 shows an example of deleting a measurement identity. When ameasurement identity2 902 is deleted, a measurement on a measurementobject associated with the measurement identity2 902 is suspended, and ameasurement report is not transmitted. A reporting configuration or ameasurement object associated with the deleted measurement identity maynot be modified.

FIG. 11 shows an example of deleting a measurement object. When aninter-frequency measurement object 1 is deleted, a UE also deletes anassociated measurement identity3 903. A measurement on theinter-frequency measurement object 1 is suspended, and a measurementreport is not transmitted. However, a reporting configuration associatedwith the deleted inter-frequency measurement object 1 may not bemodified or deleted.

When the reporting configuration is deleted, the UE also deletes anassociated measurement identity. The UE suspends a measurement on anassociated measurement object according to the associated measurementidentity. However, a measurement object associated with the deletedreporting configuration may not be modified or deleted.

A measurement report may include a measurement identity, a measuredquality of a serving cell, and a measurement result of a neighboringcell. The measurement identity identifies a measurement object for whichthe measurement report is triggered. The measurement result of theneighboring cell may include a measured quality and a cell identity ofthe neighboring cell. The measured quality may include at least one of areference signal received power (RSRP) and a reference signal receivedquality (RSRQ).

The following description is about scaling of a mobility-relatedparameter having an effect a determination on whether to perform amovement of the UE according to a UE mobility state. When the UE passesby cells at a fast speed, a movement to neighboring cells may not beachieved at a proper time, and thus a service disabled state may occur.Therefore, the mobility-related parameter can be optimized according toa UE speed to improve the movement of the UE. As such, when the UEdetermines a mobility state (i.e., performs a mobility state estimation(MSE)), and scales a parameter related to the mobility determinationaccording to the UE mobility state, the movement of the UE can be moreeffectively supported.

The UE mobility state determined by the MSE may be divided into a highmobility state, a medium mobility state, and a normal mobility state.Each mobility state may be determined on the basis of the number oftimes of performing a handover by the UE and/or the number of times ofperforming a cell reselection.

The UE in an RRC_IDLE state performs the cell reselection when a cellreselection condition is satisfied. If the number of times of performingthe cell reselection by the UE during a specific time period T_(CRmax)exceeds a first threshold N_(CR) _(—) _(H), the UE mobility statesatisfies a condition of the high mobility state. Meanwhile, if thenumber of times of performing the cell reselection by the UE during thespecific time period T_(CRmax) exceeds a second threshold N_(CR) _(—)_(M) and does not exceed the first threshold N_(CR) _(—) _(H), the UEmobility state satisfies a condition of the medium mobility state. Ifthe number of times of performing the cell reselection by the UE duringthe specific time period T_(CRmax) does not exceed the second thresholdN_(CR) _(—) _(M), the UE mobility state satisfies a condition of thenormal mobility state. However, when the UE performs the cellreselection continuously between the two identical cells, it may not becounted as the number of times of performing the cell reselection.

The UE in an RRC_CONNECTED state reports a measurement result andperforms a handover if a specific condition is satisfied in aneighboring cell measurement. If the number of times of performing thehandover by the UE during a specific time period exceeds the firstthreshold, the UE mobility state satisfies the condition of the highmobility state. Meanwhile, if the number of times of performing thehandover by the UE during the specific time period exceeds a secondthreshold and does not exceed the first threshold, the UE mobility statesatisfies the condition of the medium mobility state. If the number oftimes of performing the handover by the UE during the specific timeperiod does not exceed the second threshold, the UE mobility statesatisfies the condition of the normal mobility state.

The UE in the RRC_IDLE or RRC_CONNECTED state may enter a correspondingmobility state if it is detected that the aforementioned mobility statecondition is satisfied. Entering the corresponding mobility state may bea process in which the UE determines that its mobility state is thecorresponding mobility state. However, if it is determined that both ofthe high mobility state condition and the medium mobility statecondition are not satisfied during the specific time period, the UE mayenter the normal mobility state.

When determining the mobility state, the UE may scale the mobilityparameter on the basis of the mobility state. The UE in the RRC_IDLEstate may scale a parameter Treselection, and the UE in theRRC_CONNECTED state may scale a parameter TimeToTrigger. The scaling maybe implemented by multiplying the parameter Treselection or theparameter TimeToTrigger by a specific scaling factor. The scaling factormay vary depending on the UE mobility state. For example, a scalingfactor at the high mobility state may be less than a scaling factor atthe medium mobility state. The scaling may not be performed in thenormal mobility state. The scaling may be performed not only by the UEbut also by the network or the cell, and information thereon may beprovided to the UE.

First, scaling applied to the parameter Treselection used for the cellreselection by the UE in the RRC_IDLE state will be described in detail.

1) In case of the normal mobility state (neither medium nor highmobility state)

-   -   Treselection is not scaled.

2) In case of the high mobility state

-   -   In E-UTRAN, scaling is performed by multiplying        Treselection_(EUTRA) by a scaling factor sf-high.    -   In UTRAN, scaling is performed by multiplying        Tsreelection_(UTRA) by the scaling factor sf-high.    -   In GERAN, scaling is performed by multiplying        Treselection_(GERA) by the scaling factor sf-high.    -   In CDMA2000 HRPD, scaling is performed by multiplying        Treselection_(CDMA) _(—) _(HRPD) by the scaling factor sf-high.    -   In CDMA2000 1xRTT, scaling is performed by multiplying        Treselection_(CDMA) _(—) _(1xRTT) by the scaling factor sf-high.

3) In case of the medium mobility state

-   -   In E-UTRAN, scaling is performed by multiplying        Treselection_(EUTRA) by a scaling factor sf-medium.    -   In UTRAN, scaling is performed by multiplying        Treselection_(UTRA) by the scaling factor sf-medium.    -   In GERAN, scaling is performed by multiplying        Treselection_(GERA) by the scaling factor sf-medium.    -   In CDMA2000 HRPD, scaling is performed by multiplying        Treselection_(CDMA) _(—) _(HRPD) by the scaling factor        sf-medium.    -   In CDMA2000 1xRTT, scaling is performed by multiplying        Treselection_(CDMA) _(—) _(1xRTT) by the scaling factor        sf-medium.

An information parameter (e.g., a scaling factor) required for scalingof the parameter Treselection by the UE in the RRC_IDLE state may beprovided to the UE by being included in system information to bebroadcast. The UE may perform scaling when the system informationincludes the information parameter for scaling.

Next, scaling applied to the parameter TimeToTrigger used for ameasurement report and/or a handover by the UE in the RRC_CONNECTEDstate will be described in detail.

1) In case of the normal mobility state (neither medium nor highmobility state)

-   -   TimeToTrigger is not scaled.

2) In case of the high mobility state

-   -   Scaling is performed by multiplying TimeToTrigger by a scaling        factor sf-high.

3) In case of the medium mobility state

-   -   Scaling is performed by multiplying TimeToTrigger by a scaling        factor sf-medium.

As described above, by applying differently scaled mobility parametersaccording to the UE mobility state, a movement can be performed in amore appropriate manner. For example, if a UE in an RRC_IDLE state movesat a fast speed, whether a condition for performing a cell reselectionis satisfied may be determined within a short time period so that thereselection to a target cell is performed rapidly. In addition, if a UEin an RRC_CONNECTED state moves at a fast speed, whether a measurementresult reporting condition is satisfied during a specific time periodmay be determined within a shorter time period and this is reported sothat a handover to the target cell is performed more rapidly.

Similarly to the aforementioned mobility state estimated through theMSE, a mobility state of the UE can be implemented in various types. Themobility state of the UE may be expressed by an actual UE speed. Inaddition, the mobility state of the UE may be expressed by the number oftimes of performing a UE's cell movement (e.g., a cell reselectionand/or a handover) counted for the MSE.

When the network recognizes the mobility state of the UE, it may have asignificant effect on a network operation. When cells are deployed on awireless communication system, small cells such as a pico cell and afemto cell may be arranged within a coverage of a macro cell. In such asituation, if the UE in motion moves to another cell by performing acell reselection or a handover, the network recognizes the mobilitystate of the UE, and is operated on the basis of a mobility of the UEaccording to thereto. In doing so, a more appropriate service can beprovided to the UE, and also a network resource can be optimally used.

If the UE stays in the RRC_CONNECTED mode for a long time period, thenetwork may collect information regarding cells which provide servicesto the UE during a corresponding time period. When the networkrecognizes a position and/or size of corresponding cells and a time atwhich the service is provided to the UE in the corresponding cell, amobility of a UE which receives a service from several cells whilestaying in the RRC_CONNECTED mode for a long time period may beestimated.

However, immediately after the UE in the RRC_IDLE mode enters theRRC_CONNECTED mode or if the UE frequently performs a state transitionto the RRC_IDLE mode and the RRC_CONNECTED mode, the network experiencesa difficulty in recognizing information regarding the mobility of theUE. Therefore, it is required a method in which the UE generates itsmobility information and reports it to the network.

FIG. 12 is a flowchart showing a method of reporting mobilityinformation according to an embodiment of the present invention.

Referring to FIG. 12, a UE generates the mobility information (stepS1210).

The mobility information generated by the UE may include at least one ofmobility history information and mobility state information.

The UE may collect the mobility history information as a part of themobility information when performing a movement. The mobility historyinformation includes information related to at least one serving cell onthe basis of a mobility of the UE. At least one serving cell may includea current serving cell and/or at least one previous serving cell. The UEmay collect information related to each serving cell as a mobilityhistory entry. Therefore, the mobility history information collected bythe UE may include at least one mobility history entry for at least oneserving cell.

The UE can generate the mobility information only when it is allowed toacquire mobility information for a specific cell. For example, unlessspecific signalling which indicates that it is not allowed to acquirethe mobility information from the specific cell is received, it may bedetermined that the acquisition of the mobility information is allowed,and the UE may generate the mobility information related to the specificcell. In this case, if there is no signalling related to whether theacquisition of the mobility information from the specific serving cellis allowed, the UE may collect mobility history information for acorresponding cell and/or may update mobility state information based ona movement to the cell.

For another example, unless the signalling which indicates that it isallowed to acquire the mobility information from the specific cell isreceived, it may be determined that the acquisition of the mobilityinformation is not allowed, and the UE may not generate the mobilityinformation related to the specific cell. In this case, only for a casewhere signalling related to whether the acquisition of the mobilityinformation from the specific serving cell is allowed is acquired, theUE may collect mobility history information for a corresponding celland/or may update mobility state information based on a movement to thecell.

Instead of signalling related to whether the acquisition of the mobilityinformation is allowed, signalling related to whether a collection ofmobility history information is allowed may be provided from a relatedcell. The UE may collect the mobility history information according towhether the collection of the mobility history information is allowed.In this case, the update of the mobility state information may bedependent on a UE implementation regardless of whether the update isallowed or not.

Each mobility history entry may include information related to aspecific serving cell. The following information may be included in theentry.

1) Cell identity of specific serving cell: It may include at least oneof a Physical Cell ID (PCI) of a specific serving cell and/or a GCI(PLMN+cell ID, (Global Cell ID)).

2) A time during which a UE stays in a specific serving cell: When in anRRC_IDLE state, the stay time may be a time in which the UE camps on asuitable cell. Alternatively, when in the RRC_IDLE state, the stay timemay be a time during which the UE camps on the suitable cell or anacceptable cell.

3) A time at which the UE moves: It may be information regarding a timeat which the UE moves to a specific serving cell through a cellreselection and/or a handover. This may be based on a time stamp. As anexample of configuring the time stamp, it may be considered a method ofrecording a time which elapses from a reference time. The reference timemay be a time at which the UE first acquires mobility information.

4) Extra information regarding a specific serving cell: Frequencyinformation, RAT information, PLMN information, etc., may correspond tothe extra information.

5) The number of cells experienced by the UE during a specific previoustime period from a current time (a time at which a corresponding historyentry is collected).

If a plurality of serving cells are configured for the UE (e.g., carrieraggregation), the UE may collect information on a PCell as the mobilityhistory information. The UE may not collect information on an SCell asthe mobility history information.

If a mobility anchor cell and a non-mobility anchor cell are configuredfor the UE, the UE may collect only the mobility anchor cell as themobility history information. The UE may not collect information on thenon-mobility anchor cell as the mobility history information. Such acase may occur when a macro cell and at least one cell are configured tothe UE for a dual connectivity, and in this case, the UE collects onlyinformation on the macro cell as the mobility history information.

The mobility state information which may be included in mobilityinformation may indicate a current mobility state of the UE. Themobility state information may indicate a mobility state estimated basedon the aforementioned MSE. Alternatively, the UE may indicate a measuredspeed of the UE. The UE may update the mobility state informationaccording to the mobility state estimation or speed measurement.

A method in which the UE generates the mobility information may slightlyvary according to a situation. Hereinafter, a method of acquiring themobility information and managing it will be described in greaterdetail.

1. Generation of Mobility Information in RRC_CONNECTED State andRRC_IDLE State

The UE may generate the mobility information in the RRC_CONNECTED stateand the RRC_IDLE state. In addition, even if the UE in motion isreleased from the RRC_CONNECTED state or the RRC_IDLE state, themobility information updated and/or collected in a corresponding statemay be maintained instead of discarding it.

The generation of the mobility information related to a specific cell inthe RRC_IDLE state or the RRC_CONNECTED state of the UE may be limitedto a case where the acquisition of the mobility information is allowed.

The UE may collect the mobility history information according to amovement. The collection of the mobility history information may beperformed when the mobility information acquisition regarding a relatedcell (or the mobility history information collection) is allowed asdescribed above. A collection object of the mobility history informationmay be a new serving cell or a previous serving cell based on themovement.

The UE may successfully perform the movement, and may collect themobility history information regarding the previous serving cell. Morespecifically, if a cell reselection to a new cell is performed in theRRC_IDLE state or if a handover to the new cell is performed in theRRC_CONNECTED state, the UE may acquire mobility history informationregarding the previous serving cell.

The UE may successfully perform the movement, and may collect themobility history information regarding the new serving cell. Morespecifically, if a cell reselection to a new cell is performed in theRRC_IDLE state or if a handover to the new cell is performed in theRRC_CONNECTED state, the UE may acquire mobility history informationregarding the new serving cell.

In addition, when the UE collects the mobility history information, anRAT of a collection object cell may be considered, and whether tocollect the mobility history information may be determined on the basisthereof. If the RAT of the collection object cell is not an interestingRAT for the collection, the UE may not collect mobility historyinformation for the cell. For example, the UE may regard LTE as theinteresting RAT, and may collect mobility history information for onlyLTE cells. If the network estimates a mobility state of the UE throughmobility information regarding cells of a specific RAT (e.g., LTE), themobility history information provided by the UE to the network may alsobe constructed of only a mobility history entry for the cells of thespecific RAT (e.g., LTE). Such a method helps to decrease a signallingload of the mobility information reported by the UE to the network.

In a case where the UE collects mobility history information regarding acell of a specific RAT, if the UE selects another RAT other than thespecific RAT, a collection of additional mobility history informationmay be suspended while maintaining mobility history information storedup to now. Alternatively, if the UE selects another RAT other than thespecific RAT, the UE may delete the mobility history information storedup to now, thereby promoting a much simpler implementation of the UE.

Alternatively, when the UE collects the mobility history information,irrespective of an RAT of a cell to which the UE is currently connected,the UE may collect mobility history information regarding the cell. Inorder to receive a specific service or due to a service coverageshortage of a cell of a current RAT, the UE may be frequently connectedto another RAT different from a currently connected RAT. For example, aUE which is connected to an LTE network may be connected to a UMTSnetwork in order to use a circuit switch network when a voice service ora text service is generated. In such a situation, if the UE configuresmobility history information by using only information regarding a cellof the LTE network, since a mobility history entry of a cell which canbe collected during the UE is connected to another RAT other than LTE isnot included, a degree of precision of a UE mobility state which can beestimated by the network through the mobility history informationtransmitted by the UE may deteriorate. If the network can estimate themobility of the UE from mobility information acquired from cells basedon a plurality of RATs, even if the UE is connected to another RAT, theUE may configure the mobility history information by using informationregarding a cell of a corresponding RAT and may report this at a latertime, so as to help the network to more precisely estimate the mobilityof the UE.

2. Generation of Mobility Information in RRC_IDLE State

The UE may generate mobility information in the RRC_IDLE state. In thiscase, if the UE enters the RRC_CONNECTED state, the generated mobilityinformation may be maintained without being discarded, or may bediscarded.

The generation of the mobility information related to a specific cell inthe RRC_IDLE state of the UE may be limited to a case where theacquisition of the mobility information is allowed.

The UE may collect the mobility history information according to amovement. The collection of the mobility history information may beperformed when the mobility information acquisition regarding a relatedcell (or the mobility history information collection) is allowed asdescribed above. A collection object of the mobility history informationmay be a new serving cell or a previous serving cell based on themovement.

The UE may successfully perform the movement, and may collect themobility history information regarding the previous serving cell. Morespecifically, if a cell reselection to a new cell is performed in theRRC_IDLE state, the UE may acquire mobility history informationregarding a previous serving cell.

The UE may successfully perform the movement, and may collect themobility history information regarding the new serving cell. Morespecifically, if a cell reselection to a new cell is performed in theRRC_IDLE state, the UE may acquire mobility history informationregarding the new serving cell.

In addition, when the UE collects the mobility history information, anRAT of a collection object cell may be considered, and whether tocollect the mobility history information may be determined on the basisthereof. This may be the same as the aforementioned description for acase where the mobility information is generated in the RRC_CONNECTED orRRC_IDLE state, and a detailed description thereof is omitted.

When the mobility information is generated as in step S1210, themobility history entry may be continuously accumulated as the UEpersistently moves, which may result in a gradual increase in a size ofthe mobility information. Accordingly, a method for allowing the UE tomanage the mobility information may be required.

The UE may manage the mobility information on the basis of an amount ofthe mobility history information to be stored. That is, the UE maycollect the mobility history entry for up to N serving cells and thenmay insert this to the mobility information. The maximum number N of themobility history entries that can be included in the mobility historyinformation may be a value determined by the network or predetermined inthe UE.

If the UE moves to a new cell in a state where mobility historyinformation regarding N serving cells is already stored in the UE, theUE may replace the oldest mobility history entry with a newly collectedmobility history entry.

Alternatively, the UE may suspend storing of a new mobility historyentry until a storage space is prepared by an amount capable of adding anew entry. That is, if a specific entry is discarded according to acondition of discarding the mobility history information, a space towhich the new entry can be added may be prepared, and the UE may beallowed to add the new entry in such a situation. In this case, whetherthe space for collecting the mobility history entry is present may beapplied as one condition of determining whether the UE is allowed tocollect the mobility history entry.

The UE may manage mobility information on the basis of a maximum time ofpreserving a mobility history entry. That is, the UE may manage aspecific mobility history entry for a specific cell according to amaximum time that can be stored in the mobility information. An entrywhich has been stored by exceeding a maximum time from a collection timemay be discarded. As such, the maximum time of preserving the mobilityhistory entry may be used as a condition for discarding the mobilityhistory entry.

Meanwhile, the UE may manage the mobility information on the basis ofthe maximum number of mobility history entries and a time of preservingthe mobility history entry.

Referring back to FIG. 12, the UE reports the generated mobilityinformation to the network (step S1220).

In an RRC_CONNECTED state, the UE may report the mobility information tothe network. When the mobility information is reported to a specificserving cell, the UE may consider whether the reporting of the mobilityinformation is allowed. That is, if it is allowed to report the mobilityinformation to the serving cell, the mobility information may bereported.

When determining whether the mobility information reporting is allowed,if specific signalling regarding whether the reporting is allowed is notacquired from the serving cell, the UE may determine that the reportingis allowed. That is, unless specific signalling indicating thatreporting of the mobility information is not allowed is received fromthe serving cell, the UE may determine that the reporting of themobility information is allowed.

Alternatively, if the specific signalling regarding whether thereporting is allowed is not acquired from the serving cell, the UE maydetermine that the reporting is not allowed. That is, only when thespecific signalling for allowing that the reporting of the mobilityinformation is allowed is received from the serving cell, the UE maydetermine that the reporting of the mobility information is allowed.

The mobility information reporting of the UE may be performed inassociation with an RRC connectionestablishment/re-establishment/re-configuration (handover) procedurebetween the UE and the network. The UE may report the mobilityinformation during the RRC connectionestablishment/re-establishment/re-configuration procedure, or may reportthis in response to a request of the network after the procedure iscomplete.

In the reporting of the mobility information, the UE may indicate to thenetwork a mobility information availability indicator indicating apresence of mobility information to be reported. Upon receiving themobility information availability indicator, the network may request theUE to report the mobility information. The UE may report the mobilityinformation to the network in response to the request. The mobilityinformation availability indicator may be transmitted to the network bybeing included in an RRC connection complete message, an RRC connectionre-establishment complete message, or an RRC connection re-configurationcomplete message. Thereafter, the UE may transmit the mobilityinformation to the network in response to a mobility informationreporting request of the network.

In the reporting of the mobility information, the UE may transmit themobility information to the network without having to transmit themobility information availability indicator. Since the mobilityinformation includes the mobility history information, a network whichis not capable of interpreting it (e.g., a legacy network) may discardthe information, and a network capable of interpreting it may understandthe mobility history information. The mobility information may betransmitted to the network by being included in the RRC connectioncomplete message, the RRC connection re-establishment complete message,or the RRC connection re-configuration complete message.

A reporting method related to the aforementioned mobility informationavailability indicator may be usefully applied to the reporting of themobility history information. Regarding the mobility information, sincethe mobility history information is greater in size than the mobilitystate information, it may be problematic if it is transmitted during theRRC connection establishment/re-establishment/re-configurationprocedure. Accordingly, it may be implemented in such a manner that themobility state information and the mobility history informationavailability indicator are transmitted during the RRC connectionestablishment/re-establishment/re-configuration procedure, andthereafter the mobility history information is transmitted in responseto a request of the network. In this case, the mobility historyinformation availability indicator may indicate a presence of mobilityhistory information to be reported.

A UE which reports the mobility information may process successfullyreported mobility information, which may be performed as follows.

1) Discarding of reported mobility information: If the mobilityinformation is reported, the UE may discard the mobility information.

2) Preserving of the reported mobility information: Even if the mobilityinformation is reported, the UE may not discard the mobility informationbut preserve it. That is, the UE may preserve the mobility informationuntil a condition of discarding the mobility information is satisfied.The mobility information is preserved even if it is reported becausethere is an advantage in that a loss of the mobility information can beprevented when the UE enters again the RRC_IDLE state after staying inthe RRC_CONNECTED state during a short time period.

Meanwhile, there is a need to propose a method for processing mobilityinformation in a case where an RLF occurs when the UE moves whilepreserving the mobility information. In this case, the UE may discardthe stored mobility information at the occurrence of the RLF. Thediscarding of the mobility information may be performed at a time ofstarting the RRC connection re-establishment procedure. If the UEsuccessfully performs the RRC re-establishment procedure with a specificcell after the RLF occurrence, the UE may not generate mobilityinformation related to the cell. Consequently, since there is no validmobility information to be reported even after the RRC connectionre-establishment for an RLF recovery, the UE does not report themobility information.

Unlike this, the UE may maintain the mobility information even if theRLF occurs. If the RRC connection re-establishment procedure starts forthe RLF recovery, the UE maintains the stored mobility information. TheUE may maintain the mobility information until a condition of discardingthe mobility information is satisfied. If the UE successfully performsthe RRC re-establishment procedure with a specific cell after the RLFoccurrence, the UE may not generate mobility information related to thecell.

According to an embodiment of the present invention, the UE collectsinformation related to performing of a movement and reports it to thenetwork. Since the UE optionally reports mobility information to thenetwork, the network may more effectively estimate a state related to amovement of the UE. Accordingly, the network may provide a configurationrelated to an operation of the UE, and may provide a more improvedservice to the UE. In addition, a network resource may be moreeffectively used.

FIG. 13 is a block diagram of a wireless device according to anembodiment of the present invention. This device may implement a UEand/or network for performing a method of reporting mobility informationaccording to an embodiment of the present invention.

A wireless device 1300 includes a processor 1310, a memory 1320, and aradio frequency (RF) unit 1330.

The processor 1310 may be configured to implement the aforementionedembodiment of the present invention with reference to the drawings. Theprocessor 1310 may be configured to acquire mobility information andreport it to a network. The processor 1310 may be configured to performa movement and to collect mobility history information related to aspecific serving cell. The processor 1310 may be configured to generatemobility state information according to a mobility group state, and toreport it to the network.

The RF unit 1330 is coupled to the processor 1310, and transmits andreceives a radio signal.

The processor 1310 and the RF unit 1330 may be implemented to be capableof transmitting/receiving a radio signal according to at least onecommunication protocol. The RF unit 1330 may include at least onetransceiver capable of transmitting and receiving the radio signal.

The processor may include Application-Specific Integrated Circuits(ASICs), other chipsets, logic circuits, and/or data processors. Thememory may include Read-Only Memory (ROM), Random Access Memory (RAM),flash memory, memory cards, storage media and/or other storage devices.The RF unit may include baseband circuits for processing radio signals.When the embodiment is implemented in software, the aforementionedscheme may be implemented as a module (process or function) thatperforms the aforementioned function. The module may be stored in thememory and executed by the processor. The memory may be placed inside oroutside the processor and may be connected to the processor using avariety of well-known means.

In the above exemplary system, although the methods have been describedbased on the flowcharts in the form of a series of steps or blocks, thepresent invention is not limited to the sequence of the steps, and someof the steps may be performed in a different order from that of othersteps or may be performed simultaneous to other steps. Furthermore,those skilled in the art will understand that the steps shown in theflowchart are not exclusive and the steps may include additional stepsor that one or more steps in the flowchart may be deleted withoutaffecting the scope of the present invention.

1-15. (canceled)
 17. A method for reporting mobility historyinformation, performed by a user equipment, UE, in a wirelesscommunication system, the method comprising: generating mobility historyinformation; and transmitting the mobility history information to anetwork, wherein, if the UE changes a cell, from a first cell to asecond cell, the mobility history information comprises an entryindicating the first cell.
 18. The method of claim 17, wherein, if theUE changes a cell from a first cell using a first radio accesstechnology, RAT, to a second cell using a second RAT, the mobilityhistory information comprises an entry indicating the first cell. 19.The method of claim 18, wherein the first RAT and the second RAT aredifferent from each other.
 20. The method of claim 17, wherein the entryindicating the first cell comprises a global cell identity or a physicalcell identity of the first cell.
 21. The method of claim 20, wherein theentry indicating the first cell further comprises: time informationindicating time spent in the first cell of the UE.
 22. The method ofclaim 17, wherein the first cell is a primary cell.
 23. The method ofclaim 17, wherein the entry indicating the first cell is included in themobility history information after removing an oldest entry of themobility history information.
 24. The method of claim 17, wherein themobility history information is generated in a radio resource control,RRC, connected state or in a RRC_idle state of the UE.
 25. The method ofclaim 17, wherein the mobility history information comprises a maximumnumber of N entries, wherein N is a positive integer.
 26. A userequipment, UE, for reporting mobility history information in a wirelesscommunication system, the UE comprising: a radio frequency, RF, unit fortransmitting and receiving a radio signal; and a processor coupled withthe RF unit, wherein the processor is configured to: generate mobilityhistory information; and transmit the mobility history information to anetwork, wherein, if the UE changes a cell, from a first cell to asecond cell, the mobility history information comprises an entryindicating the first cell.
 27. The UE of claim 26, wherein, if the UEchanges a cell from a first cell using a first radio access technology,RAT, to a second cell using a second RAT, the mobility historyinformation comprises an entry indicating the first cell.
 28. The UE ofclaim 27, wherein the first RAT and the second RAT are different fromeach other.
 29. The UE of claim 26, wherein the entry indicating thefirst cell comprises a global cell identity or a physical cell identityof the first cell.
 30. The UE of claim 29, wherein the entry indicatingthe first cell further comprises: time information indicating time spentin the first cell of the UE.
 31. The UE of claim 17, wherein the firstcell is a primary cell.